The present invention relates to a passive tank stabilizer mounted on a watergoing vessel in the athwartship direction for counteracting the roll of the vessel so that the vessel can be stabilized. More particularly, the present invention relates to a passive tank stabilizer which comprises at least two tanks or two receptacles obtained by dividing one tank into two parts, which is adapted to hold quantities of stabilizing liquid such as water, and which is capable of producing stabilizing effects over a wide range of roll frequencies of the ship.
A prior art passive tank stabilizer is disclosed in a Japanese examined patent application publication No. 28873/1971, and is constructed as shown in FIGS. 13 through 15. The tank stabilizer employs a tank containing stabilizing liquid such as water, which is mounted on a ship in the athwartship direction. The tank comprises a left end chamber 2a and a right end chamber 2b connected at their lower ends by means of a crossover duct 6 and also connected at their upper ends by means of another crossover duct 8. The stabilizing tank if filled to a predetermined level with stabilizing liquid, above the level of the lower crossover duct. The crossover duct 6 is capable of transferring the stabilizing liquid, while the crossover duct 8 is capable of passing the air therethrough. The liquid in one end chamber is transferred to another chamber, which results in a rise or a fall of the liquid level in the end chambers depending on the roll of a ship. The natural frequency of the stabilizing liquid movement is set to be higher than the inherent roll frequency of the ship. The phase difference between the natural frequency of stabilizing liquid movement and the roll frequency of the ship causes the stabilizing liquid in the end chambers of the tank to counteract the roll of the ship so that stabilizing effects are produced. However, the prior art passive tank stabilizer is capable of producing stabilizing effects over roll frequencies of the ship only higher than or equal to the inherent roll frequency of the ship, but can not stabilize the ship over roll frequencies of the ship which are lower than the inherent roll frequency of the ship.